判断题 Ⅲ段研究的动物处理，不需要饲养雌性动物至分娩并饲养其子代至离乳

单项选择题 由3 个结点可以构造出多少种不同的有向树?(北方交通) A、2 B、3 C、4 D、5

判断题 The procedure used in the partial-pivoting Gaussian elimination does not change the value of the determinant, and the sign of the determinant, which can be fixed with the knowledge of the order of pivoting elements.